The IBM PC-JR and PC-AT

The IBM Personal Computer AT and JR were Personal Computers commercialized from 1984 to 1987.

Even if in the same era, those 2 Personal Computers had 2 different feedbacks from the market: while the PC-Jr was almost considered a fail for the IBM, the PC-AT (Personal Computer - Advanced Technology) deeply innovated the computer architectures.

Properties / Models	IBM PC Jr	IBM PC AT
CPU (MHz)	4.77	6 or 8 (See Graph )
RAM (kB)	64 or 128 (up to 736)	256 or 512 (up to 16 MB)
Price ($)	1300	4000-6700
Presentation Date	1st November 1983	1984
Graphic Card	CGA	EGA

The PC-Jr had different I/O devices which could work with: cassettes, optic pens, RGB and Composite port, wired or wireless infrared 62-keys keyboard, mouse, speakers, a serial port and for gamers: it was out with 2 joystick ports!
It could read floppy disks, had a 300 bps modem and was one of the first models which could use VGA, the universal standard before the HDMI standard.
More devices was produced by third party manufacturers, The PC-Jr could use most of them.
As usual, the bigger resolution the user wanted, the less colours he could use:
with a resolution of 640x200 the colours available were 2 or 4, with a 320x200 or 160x100 resolution 4 o 16 colours could be displayed.
Remembering that we're in the end of 1983, the commercial can helps us to understand how many softwares could be installed on the PC-JR.



The PC-AT was generally better and included the functionalities of the PC-JR: with its best resolution (640x350), it could display 16 colours of the 64 available;
Its keyboard had 84 keys (still used and sold nowadays), 22 keys more than the PC-JR's keyboard.
In the most advanced version, this model had integrated a 20MB Hard Disk: The first Hard Disk which was thought for personal computers was the Seagate ST-506: it's released in the 1980 and it gives to the user 5 MB of free space.
On the motherboard we can found a battery which was used quite like today: it was used for the computer to remember date and time and also the BIOS settings needed for the boot.
Here above, the message IBM wanted to send to the customers was that the PC-AT could offer a different mean of space in everyday's life.