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Post by Zallist » Sun Mar 07, 2010 3:30 pm

How to fix Bootblock.

Edit: Rank get. ;D
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Re: Ehehe

Post by BootBlock » Sun Mar 07, 2010 3:35 pm

When an Amiga is reset, the Kickstart code selects a boot device (floppy or hard drive), loads the first two sectors of the disk or partition (the bootblock), and passes control to it. Normally this code passes control back to the OS, continuing to boot from the device or partition it was loaded from. The first production Amiga, the Amiga 1000, needed to load Kickstart from floppy disk into 256 kilobytes of RAM reserved for this purpose, but subsequent Amigas held Kickstart in ROM. Some games and demos for the A1000 (notably Dragon's Lair) provided an alternative code-base in order to use the extra 256 kilobytes of RAM for data.

A floppy disk or hard drive partition bootblock normally contains code to load the 'dos.library' (AmigaDOS) and then exit to it, invoking the GUI. Any such disk, no matter what the other contents of the disk, was referred to as a "Boot disk" or "bootable disk". (A bootblock could be added to a disk by use of the "install" command.) Some entertainment software contains custom bootblocks. The game or demo then takes control of memory and resources to suit itself, effectively disabling AmigaOS and the Amiga GUI.

The bootblock became an obvious target for virus writers. Some games or demos that used a custom bootblock would not work if infected with a bootblock virus, as the code of the virus replaced the original. The first such virus was the SCA virus. Anti-virus attempts included custom bootblocks. These amended bootblock advertised the presence of the virus checker while checking the system for tell-tale signs of memory resident viruses and then passed control back to the system. Unfortunately these could not be used on disks that already relied on a custom bootblock, but did alert users of potential trouble. Several of them also replicated themselves across other disks, becoming little more than viruses in their own right.

... and then I got off the bus.

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