Third, capacity has been greatly increased in several areas:

• The new kernel can handle (theoretically) about 4.2 billion users and groups.
• 4 gigabytes of RAM is supported on Intel® architecture.
• 16 Ethernet cards can be installed on one system.
• 10 IDE controllers can be installed on one system.
• The file size restriction of 2 gigabytes has been removed.

Resource-management code has been completely rewritten to make it much more scalable and general-purpose. This change allows for greater control over the resource-management subsystem and makes it easier to use.

Integrated Web server
Newly integrated into Linux 2.4 is a kernel Web server, khttpd. This kernel-space http daemon[1] doesn't have to exist in user-space. It sends data to kernel-space to be taken to the network connection, resulting in faster response times. The khttpd can, however, only run static pages. Apache or another httpd will have to be used to run CGI programs, because khttpd is not designed as a replacement for Web servers. If it receives a request for CGI, khttpd will pass the request to user space where a Web server can process it.

Networking
Linux 2.4 has a completely rewritten networking layer. It has been made as un-serialized as possible, to allow for better scaling. The network subsystem is redesigned for stability on multiprocessor systems and many races[2] have been eliminated. There are also many updates to the existing network driver set, as well as many new devices, including support for ATM network adapters.

The Linux 2.4 rewrite includes placing firewall and Internet protocol functions into the kernel. The network subsystem has been split into two pieces: a packet filtering layer and a network address translation (NAT) layer. Each is more generic than the corresponding previous version and allows sophisticated routing through any Linux box. The rewrite also includes a new user-space tool to manage the available functionality.

Much of the PPP (point-to-point protocol) code has undergone major rewriting and modularization. The kernel now combines the PPP layers from the ISDN layer and the serial device PPP layer (like those used for dial-up connections with modems). ISDN is updated to support many new cards. The PLIP (PPP over parallel ports) layer is improved as well and now uses the new parallel-port abstraction layer and PPP over Ethernet (PPPoE) support, a protocol used by some DSL providers.