The PCMK/B card is a PCMCIA Type II form-factor card that gives a notebook computer a way to communicate to other devices on both DH+, DH485, and remote I/O communication networks.  This card has now become obsolete due to computer technology changes and AB recommends the 1784-U2DHP.

What is PCMCIA?
The Personal Computer Memory Card International Association (PCMCIA) is an organization that defines standards for connecting peripherals to laptop or notebook computers. The standard ISA, EISA, PCI, and VLB buses are too large for laptop computers; the PCMCIA PC Card is an accepted notebook standard. Rockwell Automation is a registered member of PCMCIA and developed the PCMK Communication Card (cat. no. 1784-PCMK/B)

What is a PC Card? Since personal computers have become smaller, a need for smaller storage media developed. The PC card is a small form-factor adapter that adds memory, storage, and I/O capabilities to these smaller computers. All PC cards measure the same length and width, 54.0 mm x 85.6 mm (2.13 in. x 3.37 in.), but differ in thickness at the center. The thickness at the connector end and along the rails is the same for all types of PC cards.

All three types of PC cards use the same 68-pin connector. The pins are in two parallel rows of 34 pins. When inserted into the PCMCIA slot on your computer, the connector mates with a single molded socket

What does the 1784-PCMK interface to:

PLC-5:  is a 1771 processor module that provides a trusted PLC approach for industrial control. PLC-5 processors are high-speed, single-slot processors used for control and information processing. They are designed for larger sequential and regulatory control applications with specialized I/O requirements and/or the need to coordinate with other processors and devices.

PLC-5 processors are available in a range of I/O capacity and memory size, and can be connected in a variety of networks for distributed processing and distributed I/O. The 1771 I/O products offer a full range of digital and analog I/O (including intelligent I/O) in a rugged modular assembly.

ANC-120e, Alternative USB to DH+ Cable

ANC120e 300x115 - 1784-PCMK

ANC-120e, USB to AB Data Highway Plus RSLINX PLC Programming Cable, alternative to the 1784 -U2DHP.  This high performance cable uses the AB Controllogix Ethernet Driver for fast communications access to PLC-5 & SLC 5/04s

$1,495 USD List.

ANC-120e Product Review from http://theautomationblog.com/usb-to-data-highway-plus-using-the-anc-120e-a-lower-cost-alternative-to-the-1784-u2dhp/