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zulfi123786
September 6th, 2013, 01:37 AM
Hi,

I remember old school days where we used DOS computers and had to insert a 5' inch floppy to boot the PC, today I wonder why always a floppy was needed to boot and why cant it boot from the hard disk.

Thanks,
Zulfi

Caluser2000
September 6th, 2013, 01:47 AM
Because there was no hard drive fitted to the machine in question.

Chuck(G)
September 6th, 2013, 08:25 AM
Indeed, I know of a few older (pre-PC) systems where booting could not be performed from the hard disk, but had to be done by floppy or (older) tape or cards.

zulfi123786
September 6th, 2013, 08:30 PM
That is what keeps me wondering why boot could not be performed from hard disk

krebizfan
September 6th, 2013, 09:11 PM
Well, with the Wang system I used back in 1982, the boot floppy contained login information instead of having the minicomputer display a prompt. Was supposed to make unauthorized entry slightly more challenging.

A lot of PC based educational software was designed to be launched from bootable diskettes to prevent the student from doing anything else which became a bit silly as the systems being purchased had hard disks that never saw use.

For some older systems, the design happened before the hard disk was available. The boot can only happen with the devices the system knew about. Not having worked with the 1960s era mainframes I don't know if it really was as Rube Goldbergish as sometimes described where switches are flipped which activates the (paper) tape or card which then transfers control to fast storage that contains the software and operating system users would recognize.

vwestlife
September 6th, 2013, 09:50 PM
Indeed, I know of a few older (pre-PC) systems where booting could not be performed from the hard disk, but had to be done by floppy or (older) tape or cards.

The first two ROM BIOS revisions of the IBM PC don't support booting from a hard drive, either. There were some aftermarket hard drives released for the PC during that time, but they required a boot disk.

As quoted from a Usenet post dated 1986, "If you have an older PC, with 64K on the motherboard and a serial number under 300,000, you need to get the hard disk BIOS from IBM, 'BIOS Kit ROM Module', P/N 1501005, to boot from the hard disk."

Chuck(G)
September 6th, 2013, 10:43 PM
ROMs were small and not very general in the old CP/M days. You were lucky in the old mainframe days if you even had any sort of ROM. Here's the "ROM" of a system I used for years:

http://ed-thelen.org/comp-hist/6600DeadStartPanel-.jpg

On my S100 system, at first I had a 32-byte bipolar ROM. Not nearly enough for a hard disk boot.

NeXT
September 6th, 2013, 11:07 PM
DEC sold diode matrix boards that could hold enough code to bootstrap the system.

MikeS
September 7th, 2013, 07:32 AM
That is what keeps me wondering why boot could not be performed from hard diskI thought "Because there was no hard drive fitted to the machine in question" and/or "The first two ROM BIOS revisions of the IBM PC don't support booting from a hard drive" explained it rather well...

MikeS
September 7th, 2013, 07:47 AM
DEC sold diode matrix boards that could hold enough code to bootstrap the system.Sorta like this? :
15109
That's a 10x13 inch PROM ;-)

MikeS
September 7th, 2013, 07:54 AM
DEC sold diode matrix boards that could hold enough code to bootstrap the system.Or how about a resistor matrix instead? Forget Visual BASIC, this is Visual Machine Language:
15110

NeXT
September 7th, 2013, 09:40 AM
Dave Fischer had a beautiful example.

http://www.cca.org/blog/images/diode-matrix-1.jpg

32 16-bit words


0005002 Clear R2
0052702 Bit set (PC)+ -> R2
0100247 (Data for previous instruction)
0012701 Move (PC)+ -> R1
0177170 (Data)
0130211 Bit Test R2 & (R1)
0001776 Branch if Equal -176
0112703 Move Byte (PC)+ R3
0000007 (Data)
0010100 Move R1 R0
0010220 Move R2 (R0)
0000402 Branch +2
0012710 Move (PC)+ (R0)
0000001 (Data)
0006203 Shift Right R3
0103402 Branch if Carry set +2
0112711 Move Byte (PC)+ (R1)
0111023 (Data)
0030211 Bit Test R2 & (R1)
0001776 Branch if Equal -176
0100756 Branch if Minus -156
0103766 Branch if Carry set -166
0105711 Test Byte (R1)
0100771 Branch if Minus -171
0005000 Clear R0
0022710 Compare (PC)+ (R0)
0000240 (Data)
0001347 Branch if Not Equal -147
0122702 Compare Byte (PC)+ R2
0000247 (Data)
0005500 Add Carry R0
0005007 Clear (PC)

Chuck(G)
September 7th, 2013, 10:37 AM
Well, the IBM S/360 had two principal types of ROS for microprogramming. There was the capacitor ROS (e.g. 360/30):

http://www.glennsmuseum.com/ibm/pics/capacitor_ros.jpg

and transformer ROS (e.g. 360/40):

http://www.glennsmuseum.com/ibm/pics/changing_tros.jpg

And then there was "core rope", as used in the Apollo guidance computer:

http://upload.wikimedia.org/wikipedia/commons/thumb/4/4c/Apollo_guidiance_computer_ferrit_core_memory.jpg/570px-Apollo_guidiance_computer_ferrit_core_memory.jpg