![]() Sudo dd if=_asiar-backup.img of=/dev/rdisk2 bs=4m If you want to restore a backup, you can follow exactly the same steps but you need to swap the source and target. If you want to make sure that the partitions indeed have been ejected, you can issue The SD card partitions still are known to MacOS and need to be ejected first. Once done, do not simply pull the SD card out of the Mac. You are of course free to choose whatever filename you wish. This will back up the full contents of the SD card to a file called _asiar-backup.img which gets created in the directory where the dd command gets issued. Sudo dd if=/dev/rdisk2 of=_asiar-backup.img bs=4m Knowing this it is easy to backup the SD card. So in my case the SD card was assigned to /dev/disk2 and therefore the raw device is /dev/rdisk2. ![]() The raw device corresponding to an OS device has exactly the same name prepended with an r. However, MacOS also knows about raw devices and using dd with the raw device is MUCH faster. The first layer we just saw when we checked what OS device was assigned to the SD card. for MacOS and SD cards a sensible block size is 4 megabytes which is specified as 4m. The block size specifies how many bytes get read from source and written to target at the same time. If you want to restore the SD card then source is the file and target the SD card device. If you want to back up the SD card then source is the SD card device and target a file. Source is where you want to copy the data from and target where to. The dd command requires root privileges and the general command structure is Issuing the mount command again, you can see that the partition was unmounted. dev/disk2s1 on /Volumes/BOOT (msdos, local, nodev, nosuid, noowners) When the SD card gets connected to the Mac, the BOOT partition gets mounted automatically and this needs to be unmounted for dd to work properly. In my case it shows that the SD card is the /dev/disk2 device. Proceed with caution and make sure to follow all steps and replace any device in the command examples with the ones used on your Mac!!!įirst thing to do is to see what OS device the BOOT partition is on. Failing to do so may overwrite the contents of a disk unintentionally and it will be impossible to revert. Do not copy and paste and command and execute them without making sure that your Mac is using the same device names. But before you do so, I need to write this:ĭISCLAIMER These instructions contain examples of device names that are specific to my situation. The one I used had a PDP-11/40 as the front end.įor dd, follow these following steps. Speaking of the PDP-8, my all time favorite computer (counting even today's M1 based Macs) is the PDP-10/DECsystem-20. Had all the hours I wanted to clock on that machine. The RPC-4000 was just in a corner of the room, the sign-up log book showed just a grad student using it, and me playing with it. ![]() By the time I got to use the RPC-4000, it was already 5 years old and serious number crunching was done on the campus' IBM 7094. The main attraction of that glass encased room was an EIA Hybrid Computer (analog integrators to solve differential equations, with digital input/output). The "half frame" ASI2600MC is still my favorite camera today, hah! Taken, if I am not mistaken, with an Olympus Pen EE half frame camera (film was expensive in post-war Japan, so Olympus made half frame cameras to save money). Here is the only surviving photo of me at the console (it might be a last surviving photo of Purdue's RPC-4000 :-): With non-ASCII paper tape encoding (not Baudot either). I believe Ritchie and Thompson had banged out the entire Unix OS on some ASR33. I wonder how many of today's Unix users even know why the devices in /dev are called "tty" :-). ![]()
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