Raspberry Pi 1 Model A is the successor to the original Pi 0 series. Provides a low-cost variant of Raspberry Pi. The main difference from Raspberry Pi Model 1 A is that it has a USB 2.0 port.
I think that the pi 1 A and B are discontinued. The Pi 1 A+ is the only board in the first generation of rpi boards which is smaller than its counterpart.All others are of the standard size.
Specification of Pi A:
Audio and display: HDMI port(1080p video out)
Broadcom Soc: Broadcom BCM2835
Processor: ARM1176JZF-S
Processor speeds: 700 MHz
GPU: Broadcom VideoCore IV @ 250 MHz
Ram: 256MB
Input: Usb 2.0
Power: Micro usb type B(5v,2.5A),GPIO
Usb otg port: None
Ethernet: None
Wifi: None
Bluetooth: None
Video input: CSI camera port
Usb port: 1
Audio in: Revision boards through I²S
Audio out: 3.5mm audio jack port,HDMI,I²S
Video out: HDMI,DSI display port,RCA jack,GPIO
GPIO port: 34 GPIO headers(compatible with some hats)
Reset: Software reset
Power consumption: Idle[140mA]
Video 1080p[200mA]
Specification of Pi B:
Audio and display: HDMI port(1080p video out)
Broadcom Soc: Broadcom BCM2835
Processor: ARM1176JZF-S
Processor speeds: 700 MHz
GPU: Broadcom VideoCore IV @ 250 MHz
Ram: 256MB changed to 512MB
Input: Usb 2.0 x 2
Power: Micro usb type B(5v,2.5A),GPIO
Usb otg port: None
Ethernet: 10/100 Mbit/s
Wifi: None
Bluetooth: None
Video input: CSI camera port
Usb port: 2
Audio in: Revision boards through I²S
Audio out: 3.5mm audio jack port,HDMI,I²S
Video out: HDMI,DSI display port,RCA jack,GPIO
GPIO port: 34 GPIO headers(compatible with some hats)
Reset: Software reset
Power consumption: Idle[360mA]
Video 1080p[420mA]
Specification of Pi A+:
Audio and display: HDMI port(1080p video out)
Broadcom Soc: Broadcom BCM2835
Processor: ARM1176JZF-S
Processor speeds: 700 MHz
GPU: Broadcom VideoCore IV @ 250 MHz
Ram: 256MB changed to 512MB
Input: Usb 2.0
Power: Micro usb type B(5v,2.5A),GPIO
Usb otg port: None
Ethernet: None
Wifi: None
Bluetooth: None
Video input: CSI camera port
Usb port: 1
Audio in: Revision boards through I²S
Audio out: 3.5mm audio jack port,HDMI,I²S
Video out: HDMI,DSI display port,audio jack as RCA jack,GPIO
GPIO port: 40 GPIO headers(compatible with hats)
Reset: Software reset
Power consumption: Idle[100mA]
Video 1080p[140mA]
Specification of Pi B+:
Audio and display: HDMI port(1080p video out)
Broadcom Soc: Broadcom BCM2835
Processor: ARM1176JZF-S
Processor speeds: 700 MHz
GPU: Broadcom VideoCore IV @ 250 MHz
Ram: 512MB
Input: Usb 2.0 x 4
Power: Micro usb type B(5v,2.5A),GPIO
Usb otg port: None
Ethernet: 10/100 Mbit/s
Wifi: None
Bluetooth: None
Video input: CSI camera port
Usb port: 4
Audio in: Revision boards through I²S
Audio out: 3.5mm audio jack port,HDMI,I²S
Video out: HDMI,DSI display port,audio jack as RCA jack,GPIO
GPIO port: 40 GPIO headers(compatible with hats)
Reset: Software reset
Power consumption: Idle[200mA]
Video 1080p[240mA]