Category: Programming

Custom IDE adapter for CP-4021 drive

As part of a special data recovery project, I needed to read the contents of the hard drive from an ancient Compaq LTE 8086 laptop. This hard disk, which is a Conner CP-4021, is quite an oddball. It has an unusual form factor: it’s a 3.5″ drive, but it’s slimmer and shorter than a regular drive, as if it was specifically made to fit into the LTE laptop.

Perhaps most annoyingly, the IDE connector on the drive is a very nonstandard half-pitch connector, where the pins have a horizontal pitch of 1.27mm, and a vertical pitch of 2.54mm. Inside the LTE laptop, this connects to a twin ribbon cable that goes directly to the motherboard, which basically means I have no way of connecting this drive to a “standard” modern IDE controller. (And it’s definitely an IDE drive, since the connector has 44 pins, just like any other laptop hard drive, and it has the same missing “key” pin as a standard IDE connector.)

Time to build a custom connector! After a whole lot of searching, I found a blank 50-pin header on AliExpress that should match the pitch of the drive’s connector. The 50-pin header will overshoot the 44-pin connector by a few pins, but it should still fit without issues. In an ultimate test of my fine motor skills, I soldered a spare 44-pin ribbon cable onto this 50-pin header, checking painstakingly that each pin on the female end matches the corresponding pin on the male end. To secure the delicate soldering onto the header, I covered it with clear epoxy, and let it harden overnight. And just like that, I have an adapter for connecting this ancient drive to a modern PC:

I then connected the drive to my workstation PC, and was encouraged when the drive spun up, and the PC detected the drive successfully! However, the PC didn’t seem to be able to read any actual data from the drive. After a good bit of head-scratching, and double-checking the continuity of all the pins of my adapter, and trying to connect the drive to a few other PCs, I had a last-ditch idea to rule out stuck heads or a locked spindle, which were rather common problems with older drives. I removed the top cover of the drive, exposing the heads and platter, and as the drive was spinning up, I gently turned the spindle manually away from its resting position. And wouldn’t you know it — this caused the spindle to come alive, and the drive became fully functional!

I was able to acquire an image of the drive in Linux with minimal effort (not a single bad sector!), and I’ll be keeping my fancy custom adapter in case I come across another drive like this in the future. I did a few more random Frankenstein experiments with the drive, including booting another vintage laptop from it:

…and connecting that laptop to another laptop via INTERLNK.EXE, which allows the C: drive on the “server” laptop to map as the D: drive on the “client” laptop, with the goal of transferring files from one to the other, or even dumping the entire partition, which I did with the SAVEPART tool.

The connection between the two laptops is a serial cable that I cobbled together from whatever I had on hand, which turned out to be an annoyingly short cable and, thankfully, a null-modem adapter, necessary for communication between the two serial ports. This resulted in a rather slow connection between the laptops; a parallel connection would be significantly faster, but I don’t have the appropriate cable. The INTERLNK tool (bundled with MS-DOS) worked just fine, and automatically detected the connection over the COM port.

T48 chip programmer, finally

I splurged on a proper chip programmer, the T48 by XGecu. Even though there is already a newer model of their programmer (the T56), the extra cost didn’t justify the few additional chips and features it supports, at least for me.

Along with the T48, I purchased a batch of random EEPROM chips for some initial testing and verifying of the T48 itself, and possibly for actual use in future projects. These are Winbond W27C512 chips, which have a rather unusual erase voltage of 14V and programming voltage of 12V, which will be a good exercise for the chip programmer.

The software for the T48 is for Windows only (there is an open-source alternative that supports an earlier model of this programmer (the TL866II), but it still has very limited support for the T48). And because the software is for Windows only, and especially because it requires a special driver which can only be installed with elevated privileges, I prefer to run it in a virtual machine, for reasons that I hope are obvious. Fortunately this is done very easily in VirtualBox, which supports USB passthrough effortlessly. Here it is, running in a Windows 7 (32-bit) VM, and communicating with the T48:

Since my batch of Winbond chips was suspiciously cheap, I assumed they were not “new”, but rather pulled from existing boards. And I was not mistaken: reading the chips, which worked absolutely fine, revealed that they already had contents in them:

And then, erasing and reprogramming the chips also turned out to be a breeze, which gives the T48 programmer a thumbs-up from me. As a special bonus, I removed the firmware chip from the Conner CP-4021 drive (mentioned above!) and was able to read the firmware, using one of the myriad adapters that were included with the T48 programmer.

The above chip is a Microchip 27C256 (32KB), in a PLCC-32 socket. Again, the T48 was able to read this 35-year-old chip without any issues, which makes me look forward to reading and programming many vintage and newer chips in the future.

I’ve finished some major updates to DiskDigger, as well as its companion tool FileSystemAnalyzer, to support a few more filesystems, some more obscure than others!

ReFS support

One of these filesystems represents a serious and substantial update: DiskDigger now has expanded support for ReFS, the Resilient File System introduced in recent versions of Windows Server and Windows Enterprise editions. ReFS remains totally proprietary and undocumented, so it required quite a bit of reverse-engineering to nail down the structures that it uses. I’m happy to report that DiskDigger now supports versions of ReFS starting from 3.0 (introduced in Windows Server 2016) through the very latest version 3.12 (in the latest insider build of Windows 11 Enterprise).

To be clear, DiskDigger had already been able to recover data from ReFS partitions by performing a heuristic (carving) search, which is independent of the actual filesystem on the disk. But now that it understands the data structures of ReFS, it can employ additional specific techniques to recover files more accurately from such partitions.

---

And on a lighter, more whimsical note, DiskDigger and FileSystemAnalyzer now support two other filesystem types that you’ll likely never encounter in everyday life:

RedSea filesystem

The RedSea filesystem was created by the late Terry Davis as part of his TempleOS operating system. If you’re not familiar with TempleOS, it’s an interesting rabbit hole to delve into. Literally an entire operating system built by a single person over the course of many years, TempleOS is intended to be “god’s third temple” in the form of an operating system, due to the guiding principles behind the operating system that Davis believed he was receiving from god. These principles are largely based around simplicity and purity, which is something that even the most hardened atheist like myself can appreciate. There is an expansive volume of videos in which Davis provides tutorials and explains the various features and design choices of TempleOS.

Terry was a troubled soul: he was living with uncontrolled schizophrenia which led to his eventual demise, and his videos occasionally contain some bizarre and horribly racist commentary, all of which make him more pitiable than admirable as a person. However, he was an undeniable savant at building an operating system, and I will defend the idea that we can learn something from his kernel, his compiler, and his insistence on simplicity. As a tribute to his work, I’m including support for the RedSea filesystem in DiskDigger and FileSystemAnalyzer.

The RedSea filesystem is, in many ways, the simplest filesystem possible:

• All files are contiguous! There’s no concept of fragmentation.
• There are no B-trees, no journaling, no symbolic links, no encryption, etc.
• There’s no concept of clusters; block sizes are the same as sector sizes, i.e. 512 bytes.
• Directory blocks are just a sequential list of directory entries.
• For determining where to write new files, there is simply an allocation bitmap, where each bit represents whether the corresponding block is allocated.

One other interesting feature of the RedSea filesystem is that it performs a sort of semi-automatic compression of files, using a form of LZW compression. If you give a file a name that ends with a “.Z” extension, it will be compressed when it’s written to the disk, and then uncompressed the next time it’s read from the disk (transparently to the user). This compression is also supported in DiskDigger, i.e. files recovered from a RedSea partition will be automatically uncompressed.

Commodore 64 disk images

As another fun diversion, I also added support for Commodore 64 disk images (D64 files)! The file system on these disks is thoroughly documented, and is also very simple: files are represented as a linked list of blocks (a primitive “block chain”, as it were). If you have these disk images lying around, you can now peruse their contents!

---

As with all filesystems supported by FileSystemAnalyzer and DiskDigger, these additions are read-only, since these are intended to be tools for forensic analysis, and not intended for two-way interoperability.

Usually I post updates about DiskDigger on its own website, but my most recent round of updates merits a slight technical digression.

Previous versions of DiskDigger and FileSystemAnalyzer have already had basic support for 4K-native disk drives, i.e. drives that have 4 KiB sectors instead of the usual 512 bytes. However, only recently have I been able to test this support more thoroughly, fixing a few bugs along the way. 4K-native drives have been around for a while, and in fact most modern drives already use 4K sectors natively under the hood, but simply emulate 512-byte sectors to the outside world. However, increasingly we’re seeing more drives that no longer emulate 512-byte sectors (exposing the native 4K sectors to the operating system), as well as users who are opting to reconfigure the firmware of their drive to use 4K sectors instead of 512-byte emulation. DiskDigger and FileSystemAnalyzer can now handle all of these cases when mounting and searching file systems that might be present on such disks (FAT, NTFS, ext4, etc).

I did most of my testing and experimenting using a real 4Kn drive, but some testing I did with emulated disk images. Here is how you can configure qemu to treat a disk image as a 4Kn drive:

qemu-system-x86_64.exe -machine q35 -m 8G -boot d -cdrom "linux.iso" -drive file=mydisk.vdi,if=none,format=vdi,id=D24 -device nvme,drive=D24,serial=1234,logical_block_size=4096,physical_block_size=4096

The above example boots qemu from an ISO file, which can be a Linux live DVD, and makes the hard disk become a NVMe device, which allows us to configure its physical and logical block size, which we set to 4096. Linux should detect this NVMe device automatically, which will then let you create partitions and file systems on it for experimentation.

---

The other interesting update has to do with ancient retro file systems that are supported by FileSystemAnalyzer (and by extension DiskDigger). By coincidence, I’ve been contacted by multiple people in a short span of time regarding recovering data from Xenix file systems which they’ve saved as binary disk images. One image is from an Intel System 320 Multibus System owned by Herb Johnson of retrotechnology.com, and another is from an owner of an Altos 586 system in New Zealand.

Each of these images used a slightly different version of the Xenix file system, each of which use a different structure for their superblock (and each of which is different from the Xenix/SysV support that’s built into the current version of the Linux kernel). This took a bit of effort to reverse-engineer, but ultimately wasn’t too difficult to crack and integrate into FileSystemAnalyzer. The nice thing about dealing with very old data formats is that they’re usually very simple, not to say primitive. Best of all, these Xenix images contain C header files that actually describe their own filesystem structure (can I call them eigenheaders?), which I was able to use for refining and solidifying support for these file systems.

I even learned something else that was new to me: in addition to little-endian and big-endian byte orders, there’s also something called “middle-endian” or “PDP-11-endian”, where 16-bit values are stored in native little-endian order, but 32-bit long integers are composed of two 16-bit words in big-endian order (while the numbers in both 16-bit halves are still little-endian). This was the encoding used by the PDP-11 system, and apparently also by the Altos 586 system which was running this version of Xenix. All of these variations are now supported in FileSystemAnalyzer.

I finally did something I’ve been meaning to do for a long time: get the final version of the ftape driver to work on a Linux distro that I can use in my data recovery workstations. This is for the purpose of using Linux to dump the contents of QIC-80 and similar tapes, using “floppy tape” drives, i.e. tape drives that connect to the floppy disk controller on the motherboard.

Up until this point, I’ve been using an old version of Ubuntu that has ftape pre-packaged into the kernel. The problem with this is that this version of ftape is not the latest. Development of ftape seemed to continue independently of the version that was included with the kernel. And the “last” version of ftape that is available (version 4.04a, from around July 2000) contains many enhancements over the version that was in the kernel, which seems to be 3.04, specifically compatibility with parallel port tape drives such as the Iomega Ditto 2GB.

This meant that I needed to compile the driver from source. Sounds simple enough; the driver is just a couple of loadable kernel modules. However, I would need to compile it for a version of the kernel that can boot nicely on my workstation. Browsing the source code of the driver, it appears to be intended to be compiled for kernel version 2.4.x. As an amateur kernel hacker in a previous job, I knew that even patch version changes (the third version number) in the kernel can break compilation of custom kernel modules. So, I tried to find a Linux distro that uses the earliest possible patch version of the 2.4 kernel, and still runs well on my workstation.

CentOS 3.5 to the rescue! I was able to find ISO installation media that I used to install CentOS 3.5 flawlessly onto my recovery workstation. It uses kernel version 2.4.21, which still turned out to be “too new” for compiling ftape successfully. I got a number of compilation errors, but thankfully they were all errors that were comprehensible and easy to remedy by an amateur. After just a few hacky modifications, I got the driver to compile into a loadable module!

And would you look at that – it’s able to communicate successfully with all of my floppy tape drives, as well as my parallel port Ditto 2GB drive!

Here’s my repository on GitHub that has the source code for the ftape driver, with my modifications for getting it to build in CentOS 3.5.

---

In other news, I found and restored an old ThinkPad X131e, which came to me as a Chromebook, i.e. with ChromeOS installed. In order to remove ChromeOS and install a regular Linux distro, I had to overwrite it with custom firmware that allows installing other operating systems. And in order to overwrite the firmware, I had to disassemble it and flip a physical write-protect switch that allows the firmware to be written. Why do they do this?! Anyway, with the latest version of the lightweight Xubuntu installed, this tiny thing works beautifully, and can now have a second life.